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Old 12th June 2013, 11:11 PM   #31
45 is offline 45  Italy
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Quote:
Originally Posted by llwhtt View Post
The schematic that 45 posted is an old Michaelson and Austin TVA-???, NOT a Quicksilver.

Craig
Yes, it's a mistake in fact there is SS rectifier. The QS had the 12FQ7's and a huge input cap as well in the power supply but with tubes! Rubbish anyway... The Michealson is even worse sound-wise.

Last edited by 45; 12th June 2013 at 11:21 PM.
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Old 12th June 2013, 11:20 PM   #32
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Originally Posted by john65b View Post
Palustris, that is not an 8417, but the KT88 schematic....is the transformer impedance 4200 ohm? What is the tube compliment? Sorry, not familiar with that amp...
The QuickSilver were made with KT88's as well. 4.2K will work good.
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Old 12th June 2013, 11:24 PM   #33
llwhtt is offline llwhtt  United States
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After the "good" 8417s dried up the KT88s were used.

Craig
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Old 14th June 2013, 12:51 PM   #34
john65b is offline john65b  United States
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Sounds like there are quite a few not impressed wiith the 8417 design.

I am considering the Peter Millet "Universal Input" PCB (need to confim it fits in my chassis). It has a pair of 6SN7 on input (I have quite a few) and looks to be an all in one option (kinda like my Aikido). I could choose the SS or Tube rectifier on PCB...is this a "Much Preferred" Design of the 12AX7/12BH7 Quicksilver design??

See schematic.

Question - (I may just send Pete an email thru ebay where he is selling these PCBs)

Using the 4.2k 60W Edcor Output tranny and a 450V B+, I should still get around 60 watts with this front end, correct?

I could omit input transformers and go Balanced in, correct?

If I go Single Ended in, and Ground the neg input, will it change the amp output if all else the same?

Sorry for the lame questions...
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File Type: pdf UNIAMP2_sch.pdf (138.6 KB, 59 views)
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Old 14th June 2013, 06:24 PM   #35
john65b is offline john65b  United States
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OK, just realized the transformers do the phase splitting..why would you need one if you had balanced inputs? Am I missing something here?

I also just realized have a 1:1 transformer but it is 600ohm:600ohm (if I remember correctly - a Sescom MI-14?)

Likely not high enough on the input?
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Last edited by john65b; 14th June 2013 at 06:33 PM.
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Old 23rd September 2013, 09:15 PM   #36
john65b is offline john65b  United States
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OK, Next question for the 8417

I finally started the build and have the chassis complete...pics later...it will look pretty sweet...

I have a pair of NOS Sylvania 8417....is it worth buying two more Sylvanias ($140) for the other monoblock, or sell the 8417 and buy a quad of KT120?
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Old 4th October 2013, 05:50 PM   #37
john65b is offline john65b  United States
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Bah! I will stick with the original 8417 design -I even bought a quad of 8417 Sylvania tubes...simple changes: dual bias adjustments, and maybe a 6922 instead of the 12BH7, and some of those nice Russian .22uf/600V mylar coupling caps...Some pics (finally!) Just need to solder everything together...looking good so far...
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File Type: jpg IMG_0080.jpg (513.0 KB, 167 views)
File Type: jpg IMG_0081.jpg (530.3 KB, 148 views)
File Type: jpg IMG_0082.jpg (548.6 KB, 138 views)
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Old 5th October 2013, 03:17 PM   #38
roline is offline roline  United States
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Kt120's are harder to drive, you would have to have a really good driver..... Perhaps a MosFet follower to ensure adequate drive......
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Old 9th October 2013, 12:09 PM   #39
john65b is offline john65b  United States
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Hello all, I have a quick question - these 8417 are to be biased at 100ma (50ma each tube). I am planning separate bias pots and meter points per 8417 output tube. Does the 50k bias pot have this current running through it? Reason I am asking I am trying to size the pot (1/4 watt? 1/2 watt 2 watt?). If I do the math, I should have around (60V - 15V) = 45V across the 50k pot so 45*45/ 50,000=.04 watts...but if the entire 50ma current goes through the 50k pot, we are talking a lot of wattage

The ones I normally see for fixed bias are usually only 1/4 watt.
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Old 9th October 2013, 02:37 PM   #40
kevinkr is offline kevinkr  United States
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I use 2W locking pots for bias, usually ETI purchased from mouser. Search on RV4LYSA503A at mouser.com and you will get the 50K locking pot. Only the bias currrent of nearly a mA flows through this pot.
Conservatively rated and reliable, I have never had a RV4LYSA series pot fail on me. (Made also by Ohmite and CTS)

I would recommend a lower value pot frankly of 5K or 10K with more current flowing through it. This will make the bias less prone to changing due to grid current, for the same reason adhere to the recommendations about max grid circuit resistance for the 8417.
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